<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>角度</title>
</head>
<body>
<canvas id="myCanvas" width="200" height="100"
style="border: 1px solid red"></canvas>
<script type="text/javascript">
    var c = document.getElementById("myCanvas");
    var cxt = c.getContext("2d");
    cxt.moveTo(10,10);
    cxt.lineTo(150,50);
    cxt.lineTo(10,50);
    cxt.stroke();
</script>
</body>
</html>